[code_duck]

Apple describes how the Right Way here http://support.apple.com/kb/ht1528 but I'm sure I've never seen Directory Utility before. However, in the Edit menu they reference, it said 'Disable Root User', not Enable, so it's been activated somehow. Perhaps doing sudo passwd did it, though I don't recall setting it up through an unofficial method such as that on my Mac. I'm not really comfortable hacking around on MacOS since it's a bit different than Linux, being a BSD, and the extent of integration between traditional text file style configuration and Apple's GUI stuff is unclear to me.

[lloeki]

I previously enabled it via Directory Utility, but disabled it again and tried it for you:

    $ sudo passwd
    Changing password for root.
    New password:
    Retype new password:
    passwd: Unable to change the password for record root.  Credential verification failed because account is disabled.
    $ 

So there you have it: you couldn't have done it this way.